1. Field of the Invention
The present invention relates to an image scanning apparatus which can effect a sub-scanning operation by relatively and intermittently moving a main scanning unit and a recording medium stepwise, and can record or read an image by driving the main scanning unit each time the sub-scanning is stopped.
2. Description of the Prior Art
A number of image recording apparatuses for recording an image in an image scanning apparatus have been developed nowadays, which are each mounted with a digital exposure system. Generally, in the digital exposure system, an image is recorded on a recording medium in such a manner that a light beam outputted from a semiconductor laser is modulated with image data and the light beam is deflected by high-speed rotation of a polygon mirror (main scanning), and further the light beam reflected by the polygon mirror is subjected to sub-scanning with use of a galvano-mirror or the like, or the above main scanning is effected repeatedly while moving the recording medium (or moving the recording medium stepwise). In this case, as the recording medium, a photosensitive drum electrified by a corona discharge, a photosensitive material or the like may be used. Also, in place of the semiconductor laser, other light emitter such as an LED may be used as a light source.
In case of repeating the above main scanning while shifting the recording medium in a stepwise manner, it is general that a stepping motor is used for activating its stepwise movement. The stepping motor is suitable for performing a highly precise positioning because a stop position of the recording medium can be controlled according to pulse control.
A transmission system is usually interposed between a rotary shaft of the stepping motor and a conveying roller for carrying the recording medium, and a rotational speed of the stepping motor is transmitted to the conveying roller so as to be decelerated.